Personal audio devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuitry often includes a power amplifier for driving an audio output signal to headphones or speakers.
One particular characteristic of a personal audio device which may affect its marketability and desirability is the dynamic range of its audio output signal. Stated simply, the dynamic range is the ratio between the largest and smallest values of the audio output signal. One way to increase dynamic range is to apply a high gain to the power amplifier. However, noise present in an audio output signal may be a generally monotonically increasing function of the gain of amplifier A1, such that any increased dynamic range as a result of a high-gain amplifier may be offset by signal noise which may effectively mask lower-intensity audio signals.
U.S. patent application Ser. No. 14/083,972, filed Nov. 19, 2013, entitled “Enhancement of Dynamic Range of Audio Signal Path,” and assigned to the applicant (Cirrus Logic, Inc.) of the present disclosure (the “'972 Application”) discloses methods and systems for enhancing the dynamic range of an audio signal path. In the '972 Application, an apparatus for providing an output signal to an audio transducer includes an analog signal path portion, a digital-to-analog converter (DAC), and a control circuit. The analog signal path portion has an audio input for receiving an analog signal, an audio output for providing the output signal, and a selectable analog gain, and may be configured to generate the output signal based on the analog signal and in conformity with the selectable analog gain. The DAC has a selectable digital gain and may be configured to convert a digital audio input signal into the analog signal in conformity with the selectable digital gain. The control circuit may be configured to select the selectable analog gain and select the selectable digital gain in accordance with one or more gain modes based on a magnitude of a signal indicative of the output signal, and may select the selectable analog gain and select the selectable digital gain so as to maintain a constant gain through the overall signal path regardless of the applicable gain mode.
Due to process variations, temperature variations, and/or other variations, the various analog gains of the analog path portion which may be selected as the selectable analog gain may deviate from their desired or ideal values. Accordingly, unless such variation is accounted for and corrected, the actual selectable analog gain applied to an audio signal may differ from that desired, and the overall signal path gain may not remain constant across the one or more gain modes. In addition, it may be desirable to account for and correct for such variation in a manner that is not detectable (e.g., audibly perceived) by an end user of a personal audio device.